QGraphicsAnchorLayout: Handle negative spacing in "setAnchorSpacing"
QGraphicsAnchorLayout: Handle negative spacing in "setAnchorSpacing"

The simplex solver cannot handle negative-sized anchors. Those
should be handled by the layout itself. This is done by inverting
such anchors and making their size positive again.

Ie. A --> B  with size -10   becomes   B --> A with size 10

Signed-off-by: Eduardo M. Fleury <54231285b1a7e6820e014049a5428d7993c4be1a@openbossa.org>
Reviewed-by: Jesus Sanchez-Palencia <8e4633f16312e749e5188f802770ff6e05014686@openbossa.org>

radekp/qt,pruiz/wkhtmltopdf-qt,radekp/qt,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,radekp/qt,igor-sfdc/qt-wk,radekp/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt,radekp/qt